1. Field of the Invention
This invention relates generally to sine wave generators, doubly balanced modulators, and multiplying type digital-to-analog converters. Specifically, the invention relates to means for generating a sine wave having a phase specified by a digital input, and means for multiplying the sinusoidal signal by an analog signal. In one advantageous application, the invention may be employed to supply quadrature sine and cosine sinusoidal signals for excitation of resolvers, Inductosyn devices or the like.
2. Background Art
A conventional method of generating a sinusoid signal from a digital source and multiplying the resultant sine wave by an analog signal is to use a multiplying digital-to-analog converter such as Analog Devices Part Number 7541 which comprises a conventional R/2R ladder network and CMOS transmission gates switching in the ladder rungs. The analog output of the digital-to-analog converter is scaled by the analog input exciting the ladder network. But since such a digital-to-analog converter is a linear device, the non-linear function of generating the sine wave must be programmed, for example in a look-up sine table. Thus, execution of the software functions in a conventional system, such as a microcontroller, requires considerable time and also consumes an output port.